(1) Field of the Invention
The invention relates to a catalyst system used for an olefin polymerization. More specifically, the invention relates to an olefin polymerization catalyst system comprising a specific transition metal compound and a specific support.
(2) Description of the Prior Art
In recent years, transition metal compounds which are soluble in inert organic solvents (catalyst for a homogenous system) have been the focused of attention as olefin polymerization catalysts. Specifically, in these catalysts, so-called metallocene compounds have been well-known. The process for polymerizing olefin by using these metallocene compounds, particularly the process for stereoregularly polymerizing .alpha.-olefin has been subjected to many improvements since the report of W. Kaminsky et al. (Japan Laid-Open SHO 58-19309; Angew. Chem., 97,507 (1985)).
In the slurry polymerization process for polymerizing olefin in an inert hydrocarbon by using the metallocene compound and an organic aluminum oxy compound as a catalyst, bulk polymerization process for polymerizing in a liquefied olefin monomer, or gas phase polymerization process for polymerizing in a gaseous olefin monomer, the polymer or an organic aluminum oxy compound which is formed in the course of polymerization adheres on the inner wall of the reactor, causes reduction of heat-removing capacity, further forms blocks in the reactor, and leads to troubles for the steady operation of polyolefin manufacturing facilities. Additionally, the polymer formed has a very small particle size, low bulk density, and problem of markedly lowering productivity.
In order to overcome these problems, a process for polymerizing olefin in the presence of a catalyst which is prepared by supporting an organic aluminum oxy compound on silica gel, alumina and other inorganic oxides and bringing it into contact with the metallocene compound, has been described in Japan Laid-Open SHO 60-35006, 61-108610, 61-296008, 63-66206 and HEI 2-173104. These inorganic oxides generally have an acid hydroxyl group on the surface and the catalyst is supported on the support by bringing the hydroxyl group into contact with the organic aluminum oxy compounds or metallocene compounds.
However, when polyolefin is prepared by using a catalyst obtained by supporting a metallocene compound and/or organic aluminum oxy compound on an inorganic oxide such as the above obtained silica gel and alumina, relatively hard inorganic materials such as silica gel support or alumina support remain in the formed item, act as a foreign matter, and results in development of fisheyes. Such phenomenon lowers the value of the product and additionally leads to clogging of the filter which is mounted on the molding machine, melt kneading machine and granulating machine, and renders steady operation difficult in industry.
Polyolefin prepared in the presence of an olefin polymerization catalyst obtained by supporting the organic aluminum oxy compound and/or metallocene compound on the above inorganic compound support, polypropylene in particular, leads to very low stereoregularity as compared with polyolefin prepared by using a homogeneous polymerization catalyst without support. Further, properties such as stiffness, impact resistance and heat resistance are lowered and generate a large problem with quality.
Activity improvement of olefin polymerization catalyst by modifying the organic aluminum oxy compound has been tried. For example, Japan Laid-Open HEI 2-78687 has disclosed a process for using a catalyst comprising metallocene compound and a benzene insoluble organic aluminum oxy compound obtained by bringing an organic aluminum oxy compound into contact with an active hydrogen containing compound. Japan Laid-Open HEI 7-53619 and 7-53620 have described a process for modifying the organic aluminum oxy compound by an organic compound such as ketoalcohol or .beta.-diketone.
Further, as to the process for modifying the organic aluminum oxy compound. Japan Laid-Open HEI 7-53620 has described a process for using a catalyst comprising a metallocene compound and the addition reaction product of an organic phosphorus compound having a specific structure and the organic aluminum oxy compound, in order to improve catalyst activity and simultaneously to prevent adhesion of formed polymer on the inner surface of the reactor.
However, these processes can not fully prevent the adhesion of polymer formed in the polymerization on the surface of the reactor.